﻿/* Copyright 2007-2009 dnAnalytics Project.
 *
 * Contributors to this file:
 * Jurgen Van Gael
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * 
 * * Redistributions of source code must retain the above copyright notice, this 
 *   list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright notice, 
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * * Neither the name of the dnAnalytics Project nor the names of its contributors
 *   may be used to endorse or promote products derived from this software without
 *   specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
using System;
using System.Collections.Generic;
using dnAnalytics.Properties;

namespace dnAnalytics.Statistics
{
    /// <summary>
    /// A class with correlation measures between two datasets.
    /// </summary>
    public static class Correlation
    {
        /// <summary>
        /// Computes the Pearson product-moment correlation coefficient.
        /// </summary>
        /// <param name="dataA">Sample data A.</param>
        /// <param name="dataB">Sample data B.</param>
        /// <returns>The Pearson product-moment correlation coefficient.</returns>
        public static double Pearson(IEnumerable<double> dataA, IEnumerable<double> dataB)
        {
            int n = 0;
            double r = 0.0;
            double meanA = dataA.Mean();
            double meanB = dataB.Mean();
            double sdevA = dataA.StandardDeviation();
            double sdevB = dataB.StandardDeviation();

            IEnumerator<double> ieA = dataA.GetEnumerator();
            IEnumerator<double> ieB = dataB.GetEnumerator();

            while (ieA.MoveNext())
            {
                if (ieB.MoveNext() == false)
                {
                    throw new ArgumentOutOfRangeException("Datasets dataA and dataB need to have the same length.");
                }

                n++;
                r += (ieA.Current - meanA) * (ieB.Current - meanB) / (sdevA * sdevB);
            }
            if (ieB.MoveNext() == true)
            {
                throw new ArgumentOutOfRangeException("Datasets dataA and dataB need to have the same length.");
            }

            return r / (n - 1);
        }
    }
}
